This invention relates to grey glass compositions and methods of making same. More particularly, this invention relates to erbium-containing grey glass compositions having low light transmittance in the UV and IR range while, at the same time, having high light transmittance in the visible range, thus making such glasses suitable for use as windows and windshields in the automotive industry and architectural field, as well as, in certain embodiments, as eyeglass lenses.
The automotive industry, for a number of years, has centered on the color grey, sometimes referred to as xe2x80x9cneutral greyxe2x80x9d, as the aesthetic color of choice for automotive windows. At the same time, this industry, as well as the eyeglass art, have demanded that transmission in the UV and IR range of the light spectrum be minimized. This is also desirable at certain times in the architectural field. Governmental regulations in the automotive industry, moreover, simultaneously insist that the visible light transmittance be at least 70% or greater in certain, if not all, vehicular windows when provided by the original equipment manufacturer of the vehicle (e.g. GM, Ford, Chrysler etc., in the U.S.A.). A need is thereby created in these diverse industries for a glass which achieves these properties.
A glass window, windshield or other glass article is said to have the desirable color xe2x80x9cgreyxe2x80x9d, sometimes referred to as xe2x80x9cneutral greyxe2x80x9d, if it manifests a dominant wavelength from about 435 nm, and preferably from about 470 nm, to less than about 570 nm, in combination with an excitation purity of less than about 4.5%. This, then, defines the meaning of the term xe2x80x9cgreyxe2x80x9d as used herein. A still more preferred range of dominant wavelength, thus defining a more preferred xe2x80x9cgreyxe2x80x9d as used herein, is about 480 nm-550 nm, and in like manner, a more preferred range of purity is about 0.2-4.5%. The appearance of such glass, thus defined, has been found to be of a truly xe2x80x9cgreyxe2x80x9d color, rather than wandering into an objectionable hew of bronze, green or purple, or some other color. This xe2x80x9cgreyxe2x80x9d color, as aforesaid, has found a unique demand in the automotive market, but it also has potential utility in the architectural and eyeglass markets as well.
At the same time that a true xe2x80x9cgreyxe2x80x9d color is to be achieved, there is the usually required need to achieve rather strict levels of light transmission defined conventionally by:
LTa as visible light transmission,
UV as ultraviolet light transmission,
IR as infrared light transmission, and
Ts as total solar transmission.
In order to specify the parameters of these characteristics, it is generally necessary to specify the thickness of the glass which is the subject of the measurement. As used herein, in this respect, the term xe2x80x9ca nominal thickness of about 1 mm-6 mm,xe2x80x9d and in certain embodiments, xe2x80x9cabout 3 mm-4 mmxe2x80x9d means that the characteristics of the glass are those experienced when the thickness of the actual glass under investigation is adjusted for that nominal thickness range. Such thickness ranges, in this respect, are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as a recognized thickness range for the automotive industry.
When measured at the specified nominal thickness (e.g. 3.2 mm or 4 mm) the important characteristic of color achieved by this invention may be reported by the conventional CIE LAB technique (see U.S. Pat. No. 5,308,805). Such a technique is reported in CIE Publication 15.2 (1986) and ASTM: E 308-90 [Ill. C 2xc2x0 observer].
xe2x80x9cLuminous transmittancexe2x80x9d (LTa) [2xc2x0 observer] is a characteristic and term well understood in the art, and is used herein in accordance with its well known meaning [see U.S. Pat. No. 5,308,805]. This term is also known as Ill. A visible transmittance (380-780 nanometers inclusive), and its measurement is made in accordance with CIE Publication 15.2 (1986) and ANSI test method Z26.1.
xe2x80x9cTotal solar energy transmittancexe2x80x9d (Ts) (300-2100 nm inclusive, integrated using Simpson""s Rule at 50 nm intervals using Parry Moon Air Mass=2) is another term well understood in the art [see U.S. Pat. No. 5,308,805]. It is used herein according to this well known meaning. Its measurement is conventional and well known.
The terms, and characteristics, of xe2x80x9cultraviolet light transmittancexe2x80x9d (% UV), xe2x80x9cinfrared energy transmittancexe2x80x9d (% IR), xe2x80x9cdominant wavelengthxe2x80x9d (DW) and xe2x80x9cexcitation purityxe2x80x9d (i.e. % xe2x80x9cpurityxe2x80x9d, or Pe) are also well understood terms in the art, as are their measurement techniques. Such terms are used herein, in accordance with their well known meaning [see U.S. Pat. No. 5,308,805].
xe2x80x9cUltraviolet transmittancexe2x80x9d (% UV) is measured herein using Parry Moon Air Mass=2(300-400 nm inclusive, integrated using Simpson""s Rule at 10 nm intervals). Such a measurement is well known in the art.
xe2x80x9cInfrared transmittancexe2x80x9d (% IR) is conventionally measured using Simpson""s Rule and Parry Moon Air Mass=2 over the wavelength range 800-2100 nm inclusive at 50 nm intervals. Such a measurement is well known in the art.
xe2x80x9cDominant wavelengthxe2x80x9d (DW) is calculated and measured conventionally in accord with the aforesaid CIE Publication 15.2 (1986) and ASTM: E 308-90. Its calculation and measurement are also well known in the art. As used herein, therefore, the term xe2x80x9cdominant wavelengthxe2x80x9d includes both the actual measured wavelength and, where applicable, its calculated complement.
xe2x80x9cExcitation purityxe2x80x9d (Pe or % xe2x80x9cpurityxe2x80x9d) is measured conventionally in accord with CIE Publication 15.2 (1986) and ASTM: E 308-90.
For automotive windows (including windshields) it is desirable that the glass have the following characteristics (when measured at a nominal thickness of about 3 mm-4 mm and preferably at about either 3.2 mm or 4 mm as the particular situation may require), and often in the ultimate product as well:
LTa, greater than about 70%
UV, less than about 42%, preferably less than about 38%
IR, less than about 37%, preferably less than about 28%
Ts, less than about 47%.
Generally speaking, the prior art has at times been able to meet these automotive requirements, including the achievement of the necessary, aesthetic xe2x80x9cgreyxe2x80x9d color by using as the essential ingredients of the colorant portion in an otherwise conventional silicate glass composition (e.g. a typical soda-lime-silica float glass composition), a combination of cobalt admixed with one or more of selenium, nickel, and cerium, along with an essential amount of iron. In many instances this combination was thought critical to achieving both a grey color and the requisite light transmission properties, or at least a xe2x80x9cneutral bronze color.xe2x80x9d See, for example, U.S. Pat. Nos. 4,101,705; 5,061,659; 5,264,400; 5,318,931; 5,380,685; and Japanese Patent JP4-280834.
Unfortunately, these prior art combinations often had various problems associated with them. For example, cerium, being a well known UV absorber when present in glass in its reduced form, Ce3+, should be avoided for the following reason. Iron is conventionally introduced into glass in the form of Fe2O3, part of which should be reduced to FeO to achieve the requisite low IR transmittance value. Cerium, which is introduced into glass in the form of CeO2, is known to oxidize divalent iron to trivalent iron either directly or by competition with any reducing agent present in the glass melt. Therefore, coexistence of iron oxide and cerium oxide will inevitably lead to a decrease in the concentration of FeO in the glass and thus will reduce its IR absorbing power.
The use of nickel in these prior art compositions presented the problem of nickel sulfide stones forming in the ultimate product. Selenium, furthermore, is difficult to retain in the glass during glass making. The loss of selenium created a difficulty in controlling the redox ratio in the glass, which ultimately adversely affected transmittance values. Without some, or all, of these aforesaid key ingredients, cobalt used by itself with the iron as the colorant portion of the glass composition, could not achieve the requisite combination of Lta and grey color as defined above.
Several attempts in the past have been made to employ the rare earth element erbium (reported conventionally as Er2O3, and used herein according to this conventional practice) as a colorant in automotive windows and other glass articles. For example, the aforesaid U.S. Pat. No. 5,264,400 reports the use of such an ingredient in glasses of both bronze and grey tinted colors. However, as reported therein, the use of cerium oxide is an essential ingredient in the composition.
As another example, the aforesaid Japanese Patent No. 280834 employs Er2O3 in a glass composition which is then said to have a xe2x80x9clow thermal expansion coefficient.xe2x80x9d The glass employs from 10-20% B2O3 and thus is properly referred to as a borosilicate glass, rather than the more conventional soda-lime-silica glasses used in automotive windows. While stating, in effect, that cobalt and nickel are optional, and no use of Se or Ce is reported, the dominant wavelength reported is accordingly rather high, i.e. from 570-610 nm, or tending toward an objectionable bronze color, even at the lower wavelengths achieved, rather than achieving a true xe2x80x9cgreyxe2x80x9d color as defined above.
Reference to the examples presented in this Japanese Patent ""834, moreover, demonstrates that to achieve the lower range of wavelengths (e.g. the lowest reported in 578 nm) the total iron content had to be kept at a very low 0.25% and the excitation purity was a very high 14.2%. This leads to the conclusion that this patent does not achieve, nor does it teach how to achieve, a true xe2x80x9cgreyxe2x80x9d glass which, through the use of a high level of iron in the colorant portion (rather than the low level of iron used), also simultaneously achieves low UV and IR and high LTa transmittances, along with a true xe2x80x9cgreyxe2x80x9d color. Indeed, in those examples which do not use cerium or some other UV absorber, and with the low levels of iron employed in those examples achieving lower dominant wavelengths, it is to be presumed that unacceptably high IR and UV transmittance values are the result.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which overcomes the above problems while achieving the requisite grey color and meets the other solar management requirements of the particular industry in which it is to be used. It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.
Generally speaking, this invention fulfills the above-described needs in the art by providing a unique glass composition, glass articles made therefrom, and a unique method of making the glass. In this respect, the unique glass compositions are comprised of a colorant portion consisting essentially of, by weight percent:
wherein the glass when measured at a nominal thickness of about 1 mm-6 mm, and preferably about 3 mm-4 mm (e.g. at 3.2 mm and 4 mm) has a dominant wavelength of from about 435 nm to less than about 570 nm and an excitation purity of less than about 4.5%.
In achieving (making) the above-described glasses having the aforesaid unique colorant portion it is preferred to include within the batch ingredients, and thus during glass formation, a reducing agent of one or more ingredients. In the practice of certain embodiments herein the reducing agent is comprised of (by weight of the batch) about 0.01-0.3 wt. % of silicon monoxide (SiO) and about 0-0.12 wt. % of metallic silicon (Si). In other embodiments the reducing agent may be selected from one or more conventional glass melt reducers such as sucrose, tin, carbon, or the like.
In this respect, it was heretofore known, as reported in U.S. Pat. No. 5,569,630 (issued to two of the inventors hereto) to use SiO as a reducing agent for the purpose of reducing cerium and obtaining a colorless UV absorbing glass which was free of iron. In the present invention, the combination of two lower valency forms of silicon; namely, one agent (optional) in the form of metallic silicon (Sixc2x0) powder, and the other, (Si2+) in the form of silicon monoxide (SiO), is utilized for the purpose of reducing the ferric ion to the ferrous ion, thereby obtaining a true xe2x80x9cgreyxe2x80x9d glass with the requisite low IR transmittance as well as low UV and high visible transmittances, but without the necessity of the use of cerium. Indeed, the preferred glasses of this invention are free of any cerium (except perhaps for an inadvertent trace amount in some instances). A distinct advantage of this combination of Si/SiO as the reducing agent is that during glass melting both agents are converted into SiO2, i.e. the main component in the preferred silicate glass matrices employed herein, without the need to add any dopant or other residue to the glass.
In this respect, certain unique glass compositions as contemplated by this invention comprise by weight percent:
In such compositions, it is preferred that they be substantially free of one or more of Ce, Co, Se and Ni. Most preferably the compositions are substantially free of all of these elements. By the term xe2x80x9csubstantially freexe2x80x9d is meant that such an element does not exist in an amount greater than a xe2x80x9ctrace amountxe2x80x9d (i.e.usually as an impurity) and is not purposely added to the mix. For the purposes of this invention the approximate upper limit for each element is as follows and below which the element is generally considered to be present only in a xe2x80x9ctrace amountxe2x80x9d. Most preferably, of course, the glass is entirely free of any measurable amount of such elements:
In such instances, where these limits are not exceeded, it may be said that such an element has no significant affect upon the relevant solar management properties of the glass, which, therefore, may be considered the true meaning of the term xe2x80x9ctrace amountxe2x80x9d as used herein.
The term xe2x80x9cconsisting essentially ofxe2x80x9d is used herein, in its conventional way, to define the essential ingredients while eliminating from use above a trace amount, other colorants as described above (e.g. Co, Se, Ce, Ni) which would significantly affect the solar management properties of the glass if present.
While not essential to the practice of this invention, in theory this invention may be said to achieve its true xe2x80x9cgreyxe2x80x9d color by recognizing (and utilizing) the known principle of color formation that an achromatic (grey) glass can be obtained by the interference of only two colors, blue and pink, which if properly done, is more appealing aesthetically (as a true xe2x80x9cgreyxe2x80x9d color) than the so-called xe2x80x9cgreyxe2x80x9d colors heretofore achieved with combinations of colorants such as Se, Co, and Ni in combination with the background of blue color given by the ferrous ion in the glass. In the present invention, the very pure hue of light blue (needed for the creation of true xe2x80x9cgreyxe2x80x9d) is obtained in the glass by the appropriate reduction of Fe2O3 to FeO (the IR absorber). This is accomplished by a properly balanced combination or amount of Si (optional) and SiO followed by the achromatization (i.e. xe2x80x9cphysical bleachingxe2x80x9d) to a true grey color as defined herein, brought about by the use of erbium oxide which provides the true pink color to create the requisite interference, resulting in the aesthetically pleasing grey color of the glass.
Further slight color correction and, if desired, further UV absorption may be achieved by the addition of titania. As noted above, TiO2 is an optional colorant and thus its amount of about 0.0%-1.0% is included in this term to demonstrate that TiO2 is contemplated as an affirmative colorant which optionally may be used above a trace amount.
The preferred glasses according to this invention generally exhibit, in combination, the following characteristics as measured at their intended nominal thickness:
a) a true xe2x80x9cgreyxe2x80x9d color as defined above;
b) a high transmittance of visible light, with an Lta usually equal to or greater than about 70%;
c) a low IR transmittance less than about 37% and preferably less than about 28%;
d) a low UV transmittance less than about 42% and preferably less than about 38%; and
e) a low total solar transmittance less than about 47%.
In the aforesaid U.S. Pat. No. 5,569,630 there is additionally disclosed the technique of using a multiple prebatch approach which employs the matrix components in one prebatch mix and a separate prebatch mix of CeO2 and the reducing agent. In yet another aspect of this invention, a unique method of making the glasses of this invention has been discovered which draws upon the teachings in U.S. Pat. No. 5,569,630 to help achieve enhancement of such characteristics as reproducibility, optimized color, and further improved UV and IR transmittances. For example, by the use of such a method it has been found that the reproducible nature of the solar management properties achieved are optimized over ordinary techniques of mixing all ingredients together in a single batch and, thereafter, simply melting the batch to form a glass. Generally speaking, these unique methods for making the glasses of this invention, as above-described, comprise the steps of:
a) forming at least two separate prebatch mixes which when mixed together form an overall batch mixture comprising:
Ingredient
sand
iron oxide
erbium oxide
metallic Si
SiO (silicon monoxide)
wherein the first prebatch mix comprises (and preferably consists essentially of):
Ingredient
iron oxide
metallic Si
SiO (silicon monoxide)
sand
and wherein any remaining prebatch mix or mixes include the remaining ingredients in the overall batch mixture,
b) mixing the first prebatch mix ingredients together separately from said remaining prebatch mix ingredients to form the first prebatch mix,
c) mixing the remaining ingredients so as to form at least one other separate prebatch mix, thereafter,
d) mixing the prebatch mixes together to form the overall batch mixture,
e) melting the overall batch mixture to form a glass therefrom, and thereafter,
f) forming the glass into the glass article.
This invention will now be described with respect to certain embodiments thereof, wherein: